My mom has taken ketotifen for a long time to help with allergies and I think some patients who had mast cell issues found it helpful to control immune cascades. She can only find it in France, pretty sure you can get it over the counter there but they will be discontinuing it soon from what I've been told. I think you can get it in US but only compounded.
If you have herx issues it could be something to look into, but there doesn't seem to be too much info on it in regards to lyme except in relation to mast cell issues.
Mentioned a bit in Dr Jaller's post, both as a mast cell stabilizer and antihistamine agent:
/lymemd.blogspot.com/2015/03/mast-cells-and-lyme.html